Babies in cabs

I read this post in Sfgate/moms a few months ago about babies and San Francisco cabs. Apparently, I am required by law to have a car seat in a cab, but the penalty falls on the passenger, not the driver. The officer interviewed for the article suggested that the penalty is not widely enforced. I'm going to stick with the bus (out of economic measures, not fear of the law,) but it is nice to know that a cabbie will pick up a parent with a child in tow.